(1) Field of the Invention
The present invention relates to a telephone terminal that performs a voice call by inputting/outputting audio based on audio signals transmitted through a telephone line network and through an Internet network from a transmitter/receiver.
(2) Background Art
These days Internet terminals allowing data communication through the Internet network are becoming widespread. Such Internet terminals include one having a function to perform a voice call (hereinafter referred to as the “Internet call function”) by inputting/outputting audio signals from/to the Internet network and inputting/outputting audio based on the audio signals from/to a transmitter/receiver device connected to the Internet terminal (e.g. a headset: a device with a microphone integrated into a headphone or an earphone).
In such an Internet terminal, audio based on the audio signals input/output from/to the Internet network may be output/input from a speaker and a microphone other than a headset. However, depending on the location of the speaker and the microphone, the audio output from the speaker may be difficult to be heard or the volume of the audio input from the microphone may be low, so that a voice call in good condition cannot be obtained in some cases. Therefore, it is usual to use the transmitter/receiver device (headset) connected to the Internet terminal to perform a voice call by the Internet call function.
However, the transmitter/receiver device, which is a dedicated device to be used for performing a voice call by the Internet call function, cannot be used for other purposes.
It is preferable that a device to be used for other purposes can also be used as a device to be used for the Internet call function, for any dedicated device for performing a voice call by the Internet call function is then no longer necessary to be provided.
An example of the device to be used for the Internet call function is a known telephone terminal that performs a voice call by inputting/outputting audio based on audio signals transmitted through the telephone line network from a transmitter/receiver. Such a telephone terminal can be used as an ordinary telephone terminal when the Internet call function is not used.
It has not been realized, however, to perform a voice call by the Internet call function using a known telephone terminal, and technology to allow such a voice call has been required.
An object of the present invention is to provide a telephone terminal and a call system to allow a voice call to be performed by the Internet call function using a known telephone terminal as well as a terminal control program to be used in the telephone terminal and the call system.